/*
 * Copyright (c) 1997, 2008, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package javax.swing.undo;

import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Vector;

/**
 * <P>StateEdit is a general edit for objects that change state.
 * Objects being edited must conform to the StateEditable interface.</P>
 *
 * <P>This edit class works by asking an object to store it's state in
 * Hashtables before and after editing occurs.  Upon undo or redo the
 * object is told to restore it's state from these Hashtables.</P>
 *
 * A state edit is used as follows:
 * <PRE>
 * // Create the edit during the "before" state of the object
 * StateEdit newEdit = new StateEdit(myObject);
 * // Modify the object
 * myObject.someStateModifyingMethod();
 * // "end" the edit when you are done modifying the object
 * newEdit.end();
 * </PRE>
 *
 * <P><EM>Note that when a StateEdit ends, it removes redundant state from
 * the Hashtables - A state Hashtable is not guaranteed to contain all
 * keys/values placed into it when the state is stored!</EM></P>
 *
 * @author Ray Ryan
 * @see StateEditable
 */

public class StateEdit
    extends AbstractUndoableEdit {

  protected static final String RCSID = "$Id: StateEdit.java,v 1.6 1997/10/01 20:05:51 sandipc Exp $";

  //
  // Attributes
  //

  /**
   * The object being edited
   */
  protected StateEditable object;

  /**
   * The state information prior to the edit
   */
  protected Hashtable<Object, Object> preState;

  /**
   * The state information after the edit
   */
  protected Hashtable<Object, Object> postState;

  /**
   * The undo/redo presentation name
   */
  protected String undoRedoName;

  //
  // Constructors
  //

  /**
   * Create and return a new StateEdit.
   *
   * @param anObject The object to watch for changing state
   * @see StateEdit
   */
  public StateEdit(StateEditable anObject) {
    super();
    init(anObject, null);
  }

  /**
   * Create and return a new StateEdit with a presentation name.
   *
   * @param anObject The object to watch for changing state
   * @param name The presentation name to be used for this edit
   * @see StateEdit
   */
  public StateEdit(StateEditable anObject, String name) {
    super();
    init(anObject, name);
  }

  protected void init(StateEditable anObject, String name) {
    this.object = anObject;
    this.preState = new Hashtable<Object, Object>(11);
    this.object.storeState(this.preState);
    this.postState = null;
    this.undoRedoName = name;
  }

  //
  // Operation
  //


  /**
   * Gets the post-edit state of the StateEditable object and
   * ends the edit.
   */
  public void end() {
    this.postState = new Hashtable<Object, Object>(11);
    this.object.storeState(this.postState);
    this.removeRedundantState();
  }

  /**
   * Tells the edited object to apply the state prior to the edit
   */
  public void undo() {
    super.undo();
    this.object.restoreState(preState);
  }

  /**
   * Tells the edited object to apply the state after the edit
   */
  public void redo() {
    super.redo();
    this.object.restoreState(postState);
  }

  /**
   * Gets the presentation name for this edit
   */
  public String getPresentationName() {
    return this.undoRedoName;
  }

  //
  // Internal support
  //

  /**
   * Remove redundant key/values in state hashtables.
   */
  protected void removeRedundantState() {
    Vector<Object> uselessKeys = new Vector<Object>();
    Enumeration myKeys = preState.keys();

    // Locate redundant state
    while (myKeys.hasMoreElements()) {
      Object myKey = myKeys.nextElement();
      if (postState.containsKey(myKey) &&
          postState.get(myKey).equals(preState.get(myKey))) {
        uselessKeys.addElement(myKey);
      }
    }

    // Remove redundant state
    for (int i = uselessKeys.size() - 1; i >= 0; i--) {
      Object myKey = uselessKeys.elementAt(i);
      preState.remove(myKey);
      postState.remove(myKey);
    }
  }

} // End of class StateEdit
